Conventional wind turbine towers typically include a tubular pole or a lattice structure to support a wind turbine at a considerable height to capture wind energy. The tubular pole configuration is relatively more simple and easier to assemble than the lattice structure. However, tubular poles use more steel than the lattice structure, resulting in a cost disadvantage with rising prices of steel.
Thus, lattice tower structures can have potential as an alternative to the tubular poles, especially for high hub applications and for wind turbines located in wind farms having challenging logistic requirements. For example, transporting the tubular tower sections to the site can be challenging because the sections can be twenty plus meters long and over four meters in diameter. As such, in some instances, a dedicated road is needed, but may not be possible. Accordingly, lattice tower structures may be utilized since they do not experience the same transportation issues.
FIGS. 1 and 2 are perspective views of a plurality of wind turbines 40 having a lattice tower structure 48 known in the art. The wind turbines 40 include a plurality of blades 42 mounted to a rotor hub 44, which in turn is rotationally supported by power generation components housed within a nacelle 46, as is well known in the art. The nacelle 46 is supported atop the lattice tower structure 48, which in the illustrated embodiments is formed by legs 50, horizontal braces 54, and diagonal braces 52. The legs 50 are typically angle iron members or pipe members, and the braces 52, 54 are typically angle iron members. The vertical supports (legs 50) are typically provided for bending loads, whereas the cross support-members 52, 54 connect the legs 50 and are typically provided for torsional loads. These lattice frame tower structures 48 are also referred to in the art as “space frame” towers. The lattice tower structure 48 may be fabricated in sections and erected at the wind turbine site. FIG. 3 is a more detailed view of the structural members of the lattice structure tower 48, and particularly illustrates the connection locations between the braces 52, 54 and the legs 50, as well as between aligned sections of the legs 50. Typically, a plurality of bolt connections 60 are utilized at these various connection locations.
In addition, as shown in FIG. 1, it is known in the art to apply a cladding material 56 over the lattice structure 48, which is typically any suitable fabric, such as an architectural fabric designed for harsh weather conditions. The cladding material 56 protects workers and equipment within the tower and provides an aesthetic appearance to the wind turbine 40.
The cladding material 56 is typically wrapped around the lattice tower structure 48 and tensioned by a set of dedicated hardware attached to the structural members. The cladding material 56, however, must be pre-formed and the dedicated hardware must be fabricated, both of which add costs to the lattice tower structure 48. Further, the cladding material 56 may relax over time, thus requiring constant maintenance to maintain the tension in the fabric to prevent wind damage.
In addition, the cladding material 56 covers the bolt connections making them difficult for operators to access. As such, typical lattice towers include more expensive nut inserts or simple pull rivets to provide for easier installation. The nut inserts, however, are expensive, and the pull rivets are not as strong as a nut and bolt configuration. Accordingly, more fasteners are required, which increase the costs of the tower.
Accordingly, an improved lattice tower covering for a wind turbine that addresses the aforementioned problems would be desired in the art.